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Trying to estimate the compression on my new to me Shovel. Cranking Compression warm, throttle full open ** 160 Rear and 158 Front **. I am planning on having a Sifton 112 made for me and Craig at Black Widow Cams said that this cam works best at 9:1 static. The duration is not that far off from what I have now.
****I found the article below on Nightrider.com and from what I gather I should be OK. Any help appreciated.****
"When modifying an engine, it is important to match the compression ratio with the duration of the cam. While additional cam duration can produce more usable power, to much duration can hurt the performance. The problem is created when too much duration results in lower cylinder compression pressures at low RPM which reduce the low RPM torque and power.
Below is a chart that provides guidelines for engine performance for a given range of static compression pressures. These should provide a good means of judging if the cam installed in the engine matches the other components.
Static Cranking Pressure Performance Implications
Less than 115 PSI Poor low speed performance, poor throttle response, hard starting. Compression Ratio and Cam not matched or worn rings, valves.
120 PSI to 145 PSI Expected range for most stock or modified street motors. This is a good range for a street motor.
145 PSI to 165 PSI Modified street motors. Static pressures in this range should produce good results. This is a good range for a street motor.
165 PSI to 180 PSI Marginal for street motors. Possible hard starting, detonation and overheating.
Over 180 PSI These are all out race engines. A street motor in this range will be trouble. Stick to the track."
****I found the article below on Nightrider.com and from what I gather I should be OK. Any help appreciated.****
"When modifying an engine, it is important to match the compression ratio with the duration of the cam. While additional cam duration can produce more usable power, to much duration can hurt the performance. The problem is created when too much duration results in lower cylinder compression pressures at low RPM which reduce the low RPM torque and power.
Below is a chart that provides guidelines for engine performance for a given range of static compression pressures. These should provide a good means of judging if the cam installed in the engine matches the other components.
Static Cranking Pressure Performance Implications
Less than 115 PSI Poor low speed performance, poor throttle response, hard starting. Compression Ratio and Cam not matched or worn rings, valves.
120 PSI to 145 PSI Expected range for most stock or modified street motors. This is a good range for a street motor.
145 PSI to 165 PSI Modified street motors. Static pressures in this range should produce good results. This is a good range for a street motor.
165 PSI to 180 PSI Marginal for street motors. Possible hard starting, detonation and overheating.
Over 180 PSI These are all out race engines. A street motor in this range will be trouble. Stick to the track."